The news that nearly eight out of 10 MPs believe Third World debt should be cancelled by the year 2000 is a measure of the impact of an extraordinary campaign. For a decade the issue of the unpayable debts of the world's poorest countries has haunted the bottom of the political agenda like a spectre. Occasionally a conscience-stricken churchman, maverick politician, or despairing aid agency would try to grasp public attention with stark statistics and heart-rending illustrations to show how debt repayment is making the poorest poorer. Nearly everyone nodded sadly in agreement but creditor governments and their agencies have done next to nothing.

Now, suddenly, Third World debt is back in the news, apparently as the result of an inspired decision to pull all those lone voices into one campaign and call it Jubilee 2000. The campaign, begun four years ago, to cancel the poorest countries' debts by the year 2000, has been fattening MPs' postbags recently to such an extent that when the charity ActionAid quizzed 98 of them on the subject, they found 77% supported it.

This weekend around 40,000 Jubilee 2000 supporters are expected to descend on Birmingham where the heads of government of the world's most powerful nations will gather for the G8 summit. A dozen coaches and

a specially-chartered Debt Buster Express train will take a tartan army of campaigners, including pipe band and Gospel choir, across the Border to join them.

They will argue that continuing aid without tackling debt is like giving a patient a blood transfusion without binding

his wounds. (At present rich nations take back #3 in debt repayments for every #1 given in aid. In Africa the figure is #4.) The best way to start the new millennium for a billion poor people is by a simple one-off cancellation of debts incurred by these countries in the 1970s, debts which have now spiralled out of

control. They argue that this would benefit not only debtors but also creditors, as it will enable poor countries to thrive and join the world economy as consumers.

It's an idea that seems to have caught the mood of the moment. The Jubilee 2000 Coalition is now active in more than 20 countries. The Scottish Coalition contains more than 30 organisations, mostly churches, charities, and trade unions.

Those who oppose the campaign argue that debt relief will be frittered away by corrupt and inefficient generals, bureaucrats, and politicians. And they say that if banks have to write off billions, commercial interests won't invest in these countries again.

To counter such arguments ActionAid yesterday warned that simply telling countries like Mozambique and Nicaragua to forget their international debts is not enough.

''The world's poorest people require a long-term solution to debt, not a short-term fix. It would be a human tragedy if temporary relief was not accompanied by genuine debt control. Credit worthiness is a really important question,'' says Nicola Crawhall, ActionAid's advocacy co-ordinator.

This weekend the charity will urge G8 leaders to set up an international watchdog to monitor and manage debt. The body should implement a five-point plan, including improvements to the way both debtors and creditors manage debt.

It would allow debtor governments to give priority to investing in economic growth and human development programmes over debt repayment. In the past, debt restruc-turing deals have been criticised for forcing poor countries to make excruciating cuts in their already inadequate health and education systems. The key feature of this watchdog would be its neutrality. In 1996 creditor nations announced a breakthrough. Accepting that some poor countries would never pay off their debts, the creditors, plus the IMF and the World Bank, announced the Highly Indebted Poor Countries (HIPC) initiative.

The problem with HIPC is that, to qualify, a country has to be both very poor and very indebted but also prospering. The scheme was based on working out the ratio of debts to exports. ''It's crazy when you're dealing with countries which don't even have the softwear to do such calculations.''

Even if they could, they wouldn't qualify because they are caught in a vicious circle: they can't invest in their industries and in training people because they are spending so much on debt repayments. Yet they can't pay their debts because they don't have the industries and infrastructure to generate foreign exchange.

The other problem is that debtor countries have to undergo six years of gruelling restructuring before any of their debts are written off. So far only Uganda has stayed the course. Oxfam has been working with creditor governments to try to make the HIPC initiative more humane. They want more timely relief in return for a monitored agreement from the debtor government to spend the money saved on social programmes.

ActionAid's Nicola Crawhall says Oxfam's idea is merely a ''bolt-on'' to HIPC, a scheme basically devised by the creditors for their own benefit. ActionAid's monitoring watchdog, which could be operated by one of the UN agencies, would be structured to balance the interests of both sides.

Besides, the countries HIPC is designed to help need relief now, not in six years' time. Tanzania spends nine times as much on debt repayment as basic healthcare. In some parts of Africa children are pulling ploughs because farmers cannot afford to replace cattle that have died.

Mozambique, Nicaragua, and Angola each have debts amounting to more than three times their entire GNP. Jubilee 2000 says that if there was ever a time ''to give and not to count the cost'', it is now.